Firearm caliber conversion system

ABSTRACT

A caliber conversion system has a frame, a slide connected to the frame and operable to reciprocate with respect to the frame, a recoil spring defining a central passage, the spring operably interposed between a selected portion of the slide in a selected portion of the frame, an elongated guide rod received in the central passage, and the guide rod having an elongated major intermediate portion having a first portion with a first diameter and a second portion with a different second diameter. The slide may define a forward portion defining an aperture receiving the guide rod, and the aperture may have a diameter between the first diameter of the rod and the second diameter of the rod. The slide may include a removable bushing defining the aperture. The bushing maybe threadedly received in a forward portion of the slide.

FIELD OF THE INVENTION

The present invention relates to firearms, and more particularly to a caliber conversion system that converts the caliber of a semi-automatic pistol from a centerfire caliber to 22LR rimfire caliber while retaining the pistol's original fire control group.

BACKGROUND OF THE INVENTION

A semi-automatic pistol is a type of handgun which uses a single chamber and barrel, with a mechanism powered by the previous shot to load a fresh cartridge into the chamber after each round is fired. One round is fired each time the trigger of a semi-automatic pistol is pulled. A semi-automatic pistol harnesses the energy of one shot to reload the chamber for the next, typically via recoil operation, blowback, or gas operation. After a round is fired, the spent casing is ejected and a new round from the magazine is loaded into the chamber, allowing another shot to be fired as soon as the trigger is again pulled. Most types of semi-automatic pistols rely on a removable magazine to store ammunition before it is fired, usually inserted inside the grip.

Many of these pistols have a frame that houses a trigger assembly and a magazine. A spring biased, movable slide assembly is then mounted on top of the frame. The slide includes a housing, a firing chamber, a firing pin assembly and a barrel. In operation, the user pulls the trigger which induces the firing pin assembly to strike a cartridge in the chamber, causing the cartridge to fire, resulting in the slug or projectile(s) travelling down the barrel. With slide-based pistols, the detonation of the cartridge also results in the slide housing recoiling backwards over the frame and barrel and then sliding forward back into the shooting position as a result of the spring biasing of the slide housing. This backwards and forwards motion of the slide housing performs several functions, including ejecting the spent cartridge casing, cocking the firing pin assembly, and loading another cartridge into the chamber when the slide housing comes forward.

Typically, slide assemblies are specific to a particular pistol and allow the shooter to only shoot the caliber of bullet that the barrel, magazine, and firing chamber are sized to receive. However, it is often desirable for shooters to be able to practice shooting with less powerful and/or less expensive ammunition. While slide assemblies on many pistols are removable, the easy interchangeability of the slide assemblies is limited.

More specifically, some pistols, such as those marketed under the name Springfield Armory® XD™, XDM™, or XD-S™, which is licensed and sold in the United States by Springfield Armory®, Inc. of Geneseo, Ill., are designed to be modular such that the various components, e.g., the slide assembly, the magazine, the trigger assembly, etc., can be easily removed from the frame of the pistol. However, while removing a slide and a magazine is relatively easy with these pistols, changing the slide and magazine to a different caliber is more complicated. Currently, these pistols include ten models in three different calibers, any of which can be the “first caliber” of the pistol for the purposes of the current invention, and five different cartridges: 9×19 mm Parabellum, 0.40 S&W 12, 0.357 SIG, 0.45 GAP, and 0.45 ACP. These are all conventional, high-powered cartridges that provide obvious advantages to the user in terms of their effectiveness on the target and provide sufficient energy to readily cycle the semi-automatic pistol.

However, it is often desirable to be able to fire 22LR rimfire ammunition in more powerful, higher caliber pistols. The lower power 22LR rimfire ammunition allows a shooter to become familiar with the feel of the pistol while shooting a round that has less recoil and is considerably cheaper than larger pistol calibers. Moreover, the reduced power of the smaller 22LR caliber rimfire ammunition allows it to be shot at smaller range facilities.

Despite the modular construction of these pistols, switching to a smaller round like a 22LR caliber rimfire is complicated by the fact that the smaller caliber may not have sufficient power to cycle the slide housing back and forth over the frame to load the next cartridge in the magazine into the firing chamber. Furthermore, accommodating a 22LR caliber rimfire cartridge in a semi-automatic pistol designed to receive a centerfire cartridge creates an additional challenge to retaining the pistol's original fire control group because the firing pin must strike the upper rim of the cartridge rather than the center.

Therefore, a need exists for a new and improved caliber conversion system that converts the caliber of a semi-automatic pistol from a centerfire caliber to 22LR caliber rimfire while retaining the pistol's original fire control group. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the caliber conversion system according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of converting the caliber of a semi-automatic pistol from a centerfire caliber to 22LR rimfire while retaining the pistol's original fire control group.

SUMMARY OF THE INVENTION

The present invention provides an improved caliber conversion system, and overcomes the above-mentioned disadvantages and drawbacks of the prior art. As such, the general purpose of the present invention, which will be described subsequently in greater detail, is to provide an improved caliber conversion system that has all the advantages of the prior art mentioned above.

To attain this, the preferred embodiment of the present invention essentially comprises a frame, a slide connected to the frame and operable to reciprocate with respect to the frame, a recoil spring defining a central passage, the spring operably interposed between a selected portion of the slide in a selected portion of the frame, an elongated guide rod received in the central passage, and the guide rod having an elongated major intermediate portion having a first portion with a first diameter and a second portion with a different second diameter. The slide may define a forward portion defining an aperture receiving the guide rod, and the aperture may have a diameter between the first diameter of the rod and the second diameter of the rod. The slide may include a removable bushing defining the aperture. The bushing maybe threadedly received in a forward portion of the slide. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims attached.

There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view of the current embodiment of the caliber conversion system constructed in accordance with the principles of the present invention with the slide in the closed position.

FIG. 2 is a side sectional view of the current embodiment of the caliber conversion system of FIG. 1 with the slide in the rearward position.

FIG. 3 is a left side view of the current embodiment of the guide rod of FIG. 1.

FIG. 4 is an enlarged partial view of the current embodiment of the guide rod and recoil spring taken along line 4 of FIG. 3.

FIG. 5 is an enlarged partial view of the current embodiment of the slide, bushing, guide rod, and recoil spring taken along line 5 of FIG. 2.

FIG. 6 is a top rear isometric fragmentary view of the current embodiment of the magazine of FIG. 1.

FIG. 7 is an exploded view of the current embodiment of the magazine of FIG. 1.

FIG. 8 is a front view of the current embodiment of the front insert of the magazine of FIG. 1.

FIG. 9 is a side sectional view of the current embodiment of the front insert taken along line 9-9 of FIG. 8.

FIG. 10 is an enlarged partial view of the current embodiment of the front insert taken along line 10 of FIG. 9.

FIG. 11 is a left side sectional view of the current embodiment of the magazine body of FIG. 6.

FIG. 12 is an enlarged partial rear sectional view of the current embodiment of the magazine body.

FIGS. 13A-13B are an enlarged partial view of the current embodiment of the magazine body taken along line 13A, 13B of FIG. 11.

FIG. 14 is a top view of the current embodiment of the magazine of FIG. 1 loaded with two cartridges.

FIG. 15 is a side sectional view of the current embodiment of the magazine of FIG. 14.

FIG. 16 is an enlarged partial view of the current embodiment of the magazine taken along line 16 of FIG. 15.

FIG. 17A is a left side view of the current embodiment of the caliber conversion system with the breech block initially contacting a cartridge.

FIG. 17B is a top view of the caliber conversion system of FIG. 17A.

FIG. 18A is a left side view of the current embodiment of the caliber conversion system with the cartridge at the release point from the feed lips of the magazine.

FIG. 18B is a top view of the caliber conversion system of FIG. 18A.

FIG. 19A is a left side view of the current embodiment of the caliber conversion system with the cartridge released from the feed lips.

FIG. 19B is a top view of the caliber conversion system of FIG. 19A.

FIG. 20A is a left side view of the current embodiment of the caliber conversion system with the cartridge partially inserted into the chamber.

FIG. 20B is a top view of the caliber conversion system of FIG. 20A.

FIG. 21A is a left side view of the current embodiment of the caliber conversion system with the uppermost cartridge of the magazine pushed down and back by the stripper rail and back-feed ramp.

FIG. 21B is a top view of the caliber conversion system of FIG. 21A.

FIG. 22A is a left side view of the current embodiment of the caliber conversion system with the cartridge chambered.

FIG. 22B is a top view of the caliber conversion system of FIG. 22A.

FIG. 23A is a left side view of the current embodiment of the caliber conversion system with the breech block having moved rearward from the position depicted in FIG. 22A after the chambered cartridge has discharged.

FIG. 23B is a top view of the caliber conversion system of FIG. 23A.

FIG. 24A is a left side view of the current embodiment of the caliber conversion system with the breech block having moved further rearward from the position depicted in FIG. 23A.

FIG. 24B is a top view of the caliber conversion system of FIG. 24A.

FIG. 25A is a left side view of the current embodiment of the caliber conversion system with the breech block having moved further rearward from the position depicted in FIG. 24A to bring the spent cartridge into contact with the ejector.

FIG. 25B is a top view of the caliber conversion system of FIG. 25A.

FIG. 25C is a rear view of the caliber conversion system of FIG. 25A with the breech block removed.

The same reference numerals refer to the same parts throughout the various figures.

DESCRIPTION OF THE CURRENT EMBODIMENT

An embodiment of the caliber conversion system of the present invention is shown and generally designated by the reference numeral 10.

FIGS. 1-5 illustrate the improved caliber conversion system 10 of the present invention. More particularly, the caliber conversion system has a slide 12, barrel 28, bushing 46, screw 60, guide rod 66, recoil spring 82, breech block 88, and magazine 118. The caliber conversion system attaches to the frame 116, and receives the standard fire control group (not shown), of a Springfield Armory® XD™ or XDM™ semi-automatic pistol. The caliber conversion system converts the pistol from its original caliber and cartridge to a 22LR rimfire cartridge. In FIG. 1, the slide is shown in the closed or “in battery” position with the pistol ready to fire. In FIG. 2, the slide is shown in the rearward recoil position after the pistol has been fired.

The slide 12 has a front 22, rear 24, right side 276, and bottom 20. The right side of the slide defines an ejection port 274. The slide defines two bores 14 and 16. The upper bore 14 extends the entire length of the slide. The lower bore 16 is located below and parallel to the upper bore, but extends a much shorter distance rearward from the front of the slide. The longitudinal forward and rearward movement of the slide is guided by rails on the frame 116 and slots in the slide.

The upper bore 14 receives a barrel 28, a breech block 88, and a striker locking plate 100. The striker locking plate has a bore 104 and is located at the rear 24 of the slide, the breech block 88 has a rear 92 that abuts the striker locking plate, and the barrel is located forward of the breech block. When the slide is in the closed position, the front 90 of the breech block closely abuts the rear 42 of the barrel. The lower bore 16 receives the screw 60, the bushing 46 and the front 68 portion of the guide rod 66 and recoil spring 82.

The barrel 28 has a front 40, a rear 42, a bottom 44, and a central bore 32. The central bore has a forward opening or muzzle 30. The rear portion of the central bore defines a chamber 34. The chamber 34 is sized to receive a 22LR rimfire cartridge in the current embodiment, and the central bore forward of the chamber is sized for the passage of a 22LR caliber bullet. The bottom rear of the barrel includes a barrel lug 36 with a slot 38.

The slot 38 is sized to closely receive a dovetail 108 that extends upward from a locking block 106. The locking block is an original component of the frame 116 of the pistol, and includes a front 112, a rear 110, and a takedown pin aperture 128. The engagement of the barrel lug 36 with the locking block restrains the barrel 28 while the slide 12 is free to move longitudinally forwardly and rearwardly between the closed and rearward recoil positions.

The breech block 88 is located within the slide 12 immediately behind the ejection port 274. The breech block has a front 90, rear 92, and bottom 94. The front bottom of the breech block includes a stripper rail 96. The stripper rail 96 has a forward facing radiused surface 130 and a rearward facing radiused surface 98. The function of the stripper rail will be described in more detail in the description of FIGS. 17A-25B.

The bushing 46 has a front 52, a rear 54, and a central bore 58. The front of the bushing includes a flange 50. The rear of the bushing has threads 48 that threadedly engage with threads 26 of the lower bore 16 of the slide 12. The central bore includes a shoulder 124 that causes the central bore to narrow rearward of the shoulder. The rear of the bushing defines a shallow bore 84.

The portion of the central bore 58 of the bushing 46 located in front of the shoulder 124 is sized to receive, but also to limit rearward movement of, the head 62 of the screw 60 relative to the bushing. The portion of the central bore of the bushing located rearward of the shoulder is sized to closely receive the front 68 narrow portion 78 of the guide rod 66 while permitting the bushing to slide longitudinally along the narrow portion of the guide rod. The front of the guide rod defines a threaded bore 56 that receives the threaded portion 64 of the screw 60. The screw 60 and bushing 46 slidably secure the narrow portion of the guide rod to the slide 12 and permit the guide rod to keep the recoil spring 82 relatively straight and out of the coil bind condition and maintain alignment of the recoil system as the slide moves forwardly and rearwardly between the closed and rearward recoil positions. The guide rod also limits the rearward movement of the bushing and provides an interface between the slide and the frame 116 to close the slide. Forward travel of the slide is stopped by the breech block 88 contacting a fully inserted, chambered cartridge or, in the case of an empty chamber, the rear face 42 of the barrel 28.

The guide rod 66 has a front 68, a rear 70, and an exterior surface 80. The rear of the guide rod includes a flange 72. In the case of the original slide, guide rod, and barrel of a Springfield Armory® XD™ or XDM™ semi-automatic pistol, the flange of the original guide rod contacts a feature on the original barrel. As the original slide recoils, the original barrel remain stationary and compresses the original recoil spring between the original barrel and the flange on the original guide rod.

The barrel 28 is trapped in the slide 12 and is not removable without taking the breech block 88 out of the slide. The breech block is held in place within the slide by roll pins. When the guide rod 66 is in place and the bushing 46 is screwed into the slide, travel is limited.

The caliber conversion system 10 cannot utilize the same arrangement of parts to constrain the guide rod 66 as the original parts of the pistol because the caliber conversion system utilizes a rimfire cartridge instead of the centerfire cartridge utilized by the original parts of the pistol. In order to retain the original fire control group of the pistol, the barrel 28 and guide rod have to be lowered relative to the fire control group so the firing pin (not shown) can strike the upper rim of the 22LR rimfire cartridge. As a result, there is insufficient clearance for the rear flange 72 of the guide rod to contact the barrel lug 36. Instead, rearward movement of the guide rod with respect to the frame is prevented by contact between the flange and the flat portion 134 of a semicircular takedown pin 132 received within the takedown pin aperture 128 of the locking block 106.

The exterior surface of the guide rod has a flat portion 76 and a radiused portion 120 that are located between the narrow portion 78 and a wide portion 74. The flat portion is at a 120° angle relative to the exterior surface of the narrow portion of the guide rod in the current embodiment. The radiused portion has a radius of 0.025 in the current embodiment.

The recoil spring 82 encircles the exterior surface of the guide rod 66 and is constrained by the flange 72 on the rear of the guide rod and the depth of the bore 84 in the rear 54 of the bushing 46, making the recoil spring fully captured. The recoil spring has a wire diameter of 0.035 inch and a wire radius of 0.0175 inch in the current embodiment. The recoil spring closely fits the wide portion 74 of the guide rod, and the narrow portion 78 of the guide rod is sufficiently large to still guide the recoil spring even though the recoil spring does not closely fit the narrow portion.

The angled flat portion 76 and radiused portion 120 on the exterior surface 80 of the guide rod 66 have a limited range of characteristics related to the wire radius of the recoil spring 82 that permit the recoil spring to ride smoothly over the flat portion and radiused portion as the recoil spring is compressed by the rearward recoil movement of the slide and as the coil spring expands to push the slide forward into the closed position. In the current embodiment, the tangency point 86 of the coil spring wire to the flat portion is 0.5 times the wire radius below the wire centerline 126, and the flat portion is 0.006 inch long. The tangency point and the angled flat portion work in combination with each other. The flat portion is tangential to the radiused portion, and preferably the tangency point, the forwardmost portion of the radiused portion, and the rearwardmost portion of the flat portion are coincident.

The tangency point 86 that enables the recoil spring 82 to ride smoothly over the flat portion 76 and radiused portion 120 ranges between about 0.3 to 0.7 times the wire radius of the recoil spring as long as the flat portion is maintained at an angle of 120°. If the radius of the radiused portion is too large, then the radiused portion presents more of a tapered edge rather than a radiused edge, which creates a tapered seat against the bushing 46 and causes the slide 12 to jam. If the radius of the radiused portion is too small, the wire of the recoil spring binds up against it and causes the slide to jam. Chamfers and small coner breaks do not work as substitutes for the flat portion and radiused portion.

The bore 84 in the rear 54 of the bushing 46 has an angled portion 122 that corresponds to the angle of the flat portion. When the slide 12 slides rearwardly along the guide rod 66, the rearward movement of the slide is stopped by the angled portion 122 of the bushing 46 impacting the angled flat portion 76 of the guide rod with a close fit. The length of the wide portion 74 of the guide rod is sufficient to prevent the recoil spring from being placed into coil bind. If the recoil spring is placed into coil bind, the recoil spring loses its spring effect and cannot return the slide to the closed position. The recoil spring 82 is wound left-handed and the bushing 46 is threaded right-handed in the current embodiment so that rotational displacement imparted by the recoil spring does not unscrew the bushing from the slide 12.

FIGS. 6-13 illustrate the improved magazine 118 of the present invention uninstalled from the caliber conversion system 10. More particularly, the magazine has a magazine body 136 having a front 158, rear 160, top 154, and bottom 254. The front defines a slot 180 that communicates with a central bore 204. The magazine body is generally U-shaped in cross-section. The top of the magazine body defines right and left feed lips 148, 150. The feed lips hold the uppermost cartridge in the magazine, preventing it from being ejected upward by the magazine spring 168. The uppermost cartridge is then stripped out forwardly to load the firearm. A rear portion of the left feed lip includes an upwardly protruding ejector 152. The bottom of the magazine body includes an outwardly protruding flange 256 along the perimeter. The interior of the magazine body immediately rearward of the slot 180 defines right and left slots 194, 204.

The slot 180 of the magazine body 136 receives a front insert 140. The front insert has a left and right ridges 190, 192. The left and right ridges are received by the right and left slots 194, 204 to secure the front insert to the magazine body, which closes off the front 158 of the magazine body. The front 184 of the front insert defines a recess 186. A magazine catch (not shown) releasably engages with the recess to removably retain the magazine 118 within the frame 116 of the pistol when the magazine is fully inserted. The top 182 of the front insert includes right and left ears 144, 146. In the current embodiment, the right and left ears have a height of 0.226 inch. The top defines a back-feed ramp 142 located between the right and left ears. In the current embodiment, the back-feed ramp forms a full radius between the right and left ears.

The central bore 204 in the magazine body 136 receives a follower 174, a spring 168, and a locking plate 166. The follower has a lateral bore 258 between the top 176 and bottom 178. The top 176 forms a narrow flat portion 196 at the front 266 and a wider angled portion 198 at the rear 268. In the current embodiment, the flat portion is 0.135 inches, and the angled portion meets the rear at an acute angle of about 64°. The top 172 of the spring pushes against the bottom of the follower to urge the follower upwards, and the bottom 170 of the spring pushes against the locking plate. The locking plate has a bottom protrusion 188 that is received within an aperture 256 in the magazine base 138 (FIG. 15) when the magazine 118 is assembled.

The magazine base 138 closes off the bottom 254 of the magazine body 136 to secure the follower 174, spring 168, and locking plate 166 within the central bore 204 of the magazine body. The top 162 of the magazine base defines a recess 164 that releasably receives the bottom 254 and flange 256 of the magazine body.

The back-feed ramp 142 has a radius from front 184 to rear 264 of 0.125 in the current embodiment (FIG. 10). The top 182 of the right and left ears 144, 146 and the front of the front insert meet at an acute angle of about 75° in the current embodiment. A front radiused portion 200 located between the top of the right and left ears and front of the front insert has a radius of 0.060 in the current embodiment. A rear radiused portion 202 located between the top of the right and left ears and rear 264 of the front insert has a radius of 0.200 in the current embodiment.

As the central bore 204 approaches the top 154 of the magazine body (FIG. 12), the central bore defines left and right shoulders 206, 208. The shoulders cause the central bore to narrow from a width at 220 of 0.438 inch to a width at 218 of 0.348 inch in the current embodiment. When the central bore opens at the top of the magazine body, the left and right radiused surfaces 210, 212 on the underside of the right and left feed lips 148, 150 cause the central bore to further narrow to a width at 216 of 0.200 inch in the current embodiment. In the current embodiment, the left and right radiused surfaces have a radius of 0.174.

The left feed lip 150 has a length at 226 between the rear 168 of the magazine body 136 and the forwardmost portion of the ejector 152 of 0.385 inch in the current embodiment (FIGS. 13A-B). The length of the top 154 of the magazine body below the ejector at 228 is 0.284 inch in the current embodiment. The ejector has a height at 224 of 0.164 inch. The radiused surface 234 below the ejector has a radius of 0.094 in the current embodiment The rearmost portion of the left feed lip below the ejector at 238 has a height of 0.073 inch. The height of the left feed lip at 222 is 0.171 inch in the current embodiment. The rearmost portion of the left feed lip meets with a tangential line extending from the forward portion of the left feed lip at an acute angle 232 of about 73.5° in the current embodiment. The radiused surface 236 below and forward of the radiused surface 234 has a radius of 0.145 in the current embodiment. The length of the left feed lip at 240 is 0.100 inch. The length of the left feed lip at 242 is 0.596 inch. The tangential line extending from the forward portion of the left feed lip meets with the front 158 of the magazine body at an acute angle 230 of about 80°. The forwardmost portion of the left feed lip meets with the front of the magazine body at an acute angle 230 of about 75°. The right feed lip 148 has the same profile as the left feed lip except for the features relating to the ejector. The right feed lip 148 has a height at 214 of 0.027 inch in the current embodiment. All of the parts of the magazine are made of aluminum in the current embodiment, with an optional metal inset in the ejector on the aluminum magazine body for increased reliability. The entire magazine can also be made of plastic. However, to enhance reliability, the all-plastic magazine would preferably include a metal insert used for the ejector or ejector face and a metal insert for the magazine catch. The all-plastic magazine could have the body molded in one piece or two depending upon the material used and the optimal manufacturing processes.

FIGS. 14-16 illustrate the improved magazine 118 of the present invention uninstalled from the caliber conversion system 10. More particularly, the magazine is shown loaded with an uppermost cartridge 246 and a lower cartridge 262. The cartridges are both 22 LR rimfire cartridges with a casing 248 having a bullet 260 protruding from the front 250. The bullet has a nose 252. The uppermost cartridge 246 is depicted with the nose of the bullet contacting the back-feed ramp 142. The back-feed ramp enables the uppermost cartridge to slide down and back into the magazine immediately after a cartridge has been chambered. This process will be described in more detail in the discussion of FIGS. 17-25.

FIGS. 17A-25B illustrate the improved caliber conversion system 10 of the present invention with the slide 12 and recoil spring 82 removed for clarity. More particularly, FIGS. 17A-25B show the sequence of events that occur as the caliber conversion system chambers a first cartridge 270 and begins to eject the spent first cartridge after the pistol is discharged. FIGS. 17A-B show the point of initial contact between the front radiused surface 130 on the stripper rail 96 of the breech block 88 with the rim 254 of the first cartridge.

FIGS. 18A-B show the first cartridge 270 at the point where the cartridge is about to be released by the right and left feed lips 148, 150. Because the right and left feed lips are so short, the bullet 260 and the front 250 of the casing 248 would be prone to moving side to side, but the presence of the right and left ears 144, 146 prevents lateral movements. Instead, the left and right ears guide the cartridge until it is controlled by the feed ramp 272. In the current embodiment, the feed ramp has a length of 0.205 inch.

FIGS. 19A-B show the first cartridge 270 in the released state. The front 90 of the breech block 88 has pushed the first cartridge sufficiently far forward that the nose 252 of the bullet 260 is constrained by the feed ramp 272, which ensures the first cartridge continues to move forwardly into the chamber 34 as the breech block continues to urge the cartridge forwardly.

FIGS. 20A-21B show the first cartridge 270 partially inserted into the chamber 34 by continued forward movement of the breech block 88. As the breech block moves forward, the now uppermost cartridge 246 is pushed forward until the nose 252 of the bullet 260 contacts either the feed ramp 272 and/or the back-feed ramp 142 on the front insert 140 of the magazine 118. Once contact occurs, the back-feed ramp enables the uppermost cartridge to slide down and back into the magazine.

FIGS. 22A-B show the first cartridge 270 fully inserted into the chamber 34 by continued forward movement of the breech block 88. The figures show the breech block in the closed position where the front 90 of the breech block abuts the rear 42 of the barrel 28. When the breech block is in the closed position, the now uppermost cartridge 246 pivots. The pivoting of the uppermost cartridge results in the rim 254 of the uppermost cartridge being higher than the rear radiused surface 98 of the stripper rail 96 of the breech block.

FIGS. 23A-B show the initial rearward movement of the breech block 88 after the first cartridge 270 is discharged. As the breech block moves rearward and withdraws the casing 248 of the spent first cartridge, the uppermost cartridge 246 is pulled back by the engagement of the rear radiused surface 98 of the stripper rail 96 of the breech block with the rim 254 of the uppermost cartridge.

FIGS. 24A-B show the continued rearward movement of the breech block 88 after the first cartridge 270 is discharged. As the breech block moves further rearward, the casing 248 of the spent first cartridge is completely withdrawn from the chamber 34. The rear radiused surface 98 of the stripper rail 96 of the breech block pushes the uppermost cartridge 246 downward in the magazine 118. The back-feed ramp 142 on the front insert 140 and the rear radiused surface of the stripper rail combined to prevent jamming and loss of velocity of the slide 12 as the uppermost cartridge is pushed downward in the magazine.

FIGS. 25A-C show the continued rearward movement of the breech block 88 after the first cartridge 270 is discharged. As the breech block moves further rearward, the rim 254 of the casing 248 of the spent first cartridge contacts the ejector 152 that is integral to the magazine body 136. The ejector ejects the casing of the spent first cartridge from the slide 12 through the ejection port 274, which enables the pistol to return to the condition illustrated in FIGS. 17A-B for the chambering of the uppermost cartridge 246.

The standard centerfire version of the original pistol features a downwardly protruding stripper rail that runs the full length of the slide from the rear to the ejection port. The original configuration places the stripper rail in contact with the sear as the slide moves the stripper rail forward and rearward as the pistol cycles. Because the current invention requires the breech block 88 to be made of lightweight aluminum to accommodate the lower powered 22LR rimfire ammunition, the sear would damage the stripper rail if the stripper rail maintained the same length as the original version. As a result, the current invention utilizes a shorter stripper rail to avoid contacting the sear. However, a potential problem occurs when the stripper rail gets in front of the rim of the uppermost cartridge in the magazine while the breech block is loading the first cartridge. The rear radiused surface on the stripper rail allows the rim of the uppermost cartridge to slide up and be forced back down into the magazine. The front radiused surface on the stripper rail provides clearance to accommodate the limited distance the magazine can be inserted into the frame because of the pistol's original ejector that is pinned to the frame. This limited insertion distance results in the magazine having a very steep feed ramp angle.

The feed lips are cut back far enough that a cartridge can pop up out of the magazine before any part of the cartridge enters the chamber. The ears on the front insert of the magazine constrain the lateral position of the cartridge to keep the cartridge aligned with the chamber and allow the slide to go forward. The feed lips do not extend even halfway forward on the cartridge. The forward edge of the feed lips is spaced apart from the rear surface of the barrel by more than the overall length of the cartridge. Otherwise, the bullet could not float freely. Conventional firearm designs strive to maintain control the rim of the cartridge by the feed lips until the nose of the bullet is in the chamber. The current invention violates this rule and achieves the unexpected result of avoiding jams that otherwise would result from the shortened stripper rail.

The flat portion of the top of the follower permits the follower to clear the stripper rail. The angled portion of the follower does not match the angle of the feed lips. The difference in angle accommodates the rim of the cartridge and keeps the casing of the cartridge against the forward edge of the feed lips.

The ejector of the current invention is integral to the magazine because there is no room for an additional ejector on the frame or a separate piece interlocked to the barrel as is done conventionally. In order to accommodate the pistol's original striker, there is insufficient wall thickness left in the breech block to accommodate an ejector. The pistol's original ejector cannot be utilized because of the need to lower the slide components to accommodate the 22LR rimfire cartridges.

For disassembly, the bushing is unscrewed and the bushing and guide rod are removed. The slide can then be retracted further than is possible during normal operation, which enables the barrel to be pivoted up into a recessed pocket in the slide. This disengages the barrel from the locking block and allows the slide to be removed by disengaging the sear and pushing the slide forward.

In operation the barrel has a small amount of float with respect to the locking block. But when the slide is fully closed, the barrel is pushed slightly forward and upward. This causes the barrel to lock up to the slide is believed to increase the overall accuracy of the caliber conversion system. Conversely, as the slide starts to retract, this allows some float to the barrel to prevent binding and accommodate manufacturing tolerances.

While a current embodiment of a caliber conversion system has been described in detail, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention. With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.

Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. 

I claim:
 1. A pistol comprising: a frame; a slide connected to the frame and operable to reciprocate with respect to the frame; a recoil spring defining a central passage, the spring operably interposed between a selected portion of the slide and a selected portion of the frame; an elongated guide rod received in the central passage; and the guide rod having an elongated major intermediate portion having a first portion with a first diameter, and a second portion with a different second diameter.
 2. The pistol of claim 1 wherein the slide defines a forward portion defining an aperture receiving the guide rod, and wherein the aperture has a diameter between the first diameter of the rod and second diameter of the rod.
 3. The pistol of claim 2 wherein the slide includes a removable bushing defining the aperture.
 4. The pistol of claim 3 wherein the bushing is threadedly received in a forward portion of the slide.
 5. The caliber conversion system of claim 1 wherein the major intermediate portion of the guide rod further comprises a transitional portion with a varying diameter ranging between the first diameter and the second diameter that connects the first portion to the second portion.
 6. The caliber conversion system of claim 5 wherein the transitional portion has a flat angled portion and a radiused portion.
 7. The caliber conversion system of claim 6 wherein the flat portion is tangential to the radiused portion.
 8. The caliber conversion system of claim 7 wherein the spring has a wire radius and a wire centerline, and wherein the spring contacts the flat portion at a tangency point that is 0.5 times the wire radius below the wire centerline.
 9. The caliber conversion system of claim 8 wherein the wire radius is 0.0175 inch.
 10. The caliber conversion system of claim 8 wherein the tangency point, a forwardmost portion of the radiused portion, and a rearward most portion of the flat portion are coincident.
 11. The caliber conversion system of claim 6 wherein the recoil spring has a wire radius and wherein the radiused portion has a radius greater than 0.3 times the wire radius of the recoil spring and a radius less than 0.7 times the wire radius of the recoil spring.
 12. The caliber conversion system of claim 11 wherein the wire radius is 0.0175 inch.
 13. The caliber conversion system of claim 11 wherein the flat portion has an angle of 120° relative to the exterior surface of the front portion of the rod.
 14. The caliber conversion system of claim 13 wherein the flat portion is 0.006 inch long and the radiused portion has a radius of 0.025.
 15. The caliber conversion system of claim 3 wherein the spring is wound left-handed and the bushing is threaded right-handed.
 16. A caliber conversion system for a pistol having a frame, the system comprising: a slide adapted for connection to the frame and operable to reciprocate with respect to the frame; a recoil spring defining a central passage, the spring operably interposed between a selected portion of the slide and a selected portion of the frame; an elongated guide rod received in the central passage; and the guide rod having an elongated major intermediate portion having a first portion with a first diameter, and a second portion with a different second diameter.
 17. The pistol of claim 16 wherein the slide defines a forward portion defining an aperture receiving the guide rod, and wherein the aperture has a diameter between the first diameter of the rod and second diameter of the rod.
 18. The pistol of claim 17 wherein the slide includes a removable bushing defining the aperture.
 19. The pistol of claim 18 wherein the bushing is threadedly received in a forward portion of the slide.
 20. The caliber conversion system of claim 16 wherein the major intermediate portion of the guide rod further comprises a transitional portion with a varying diameter ranging between the first diameter and the second diameter that connects the first portion to the second portion.
 21. The caliber conversion system of claim 20 wherein the transitional portion has a flat angled portion and a radiused portion.
 22. The caliber conversion system of claim 21 wherein the flat portion is tangential to the radiused portion.
 23. The caliber conversion system of claim 22 wherein the spring has a wire radius and a wire centerline, and wherein the spring contacts the flat portion at a tangency point that is 0.5 times the wire radius below the wire centerline.
 24. The caliber conversion system of claim 23 wherein the wire radius is 0.0175 inch.
 25. The caliber conversion system of claim 23 wherein the tangency point, a forwardmost portion of the radiused portion, and a rearward most portion of the flat portion are coincident.
 26. The caliber conversion system of claim 21 wherein the recoil spring has a wire radius and wherein the radiused portion has a radius greater than 0.3 times the wire radius of the recoil spring and a radius less than 0.7 times the wire radius of the recoil spring.
 27. The caliber conversion system of claim 26 wherein the wire radius is 0.0175 inch.
 28. The caliber conversion system of claim 26 wherein the flat portion has an angle of 120° relative to the exterior surface of the front portion of the rod.
 29. The caliber conversion system of claim 28 wherein the flat portion is 0.006 inch long and the radiused portion has a radius of 0.025.
 30. The caliber conversion system of claim 18 wherein the spring is wound left-handed and the bushing is threaded right-handed. 